sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 (Mohs); Color: Grey, black, or tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs)
Color: Grey, black, or tan
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Grey, black, or tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or via chemical precipitation from silica-rich fluids in sedimentary basins.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as decorative gravel, in road construction, and for fire-starting kits.

Geological facts

Flint is a variety of chert that has been used by humans for millions of years to create tools. It creates sparks when struck against steel, making it vital for early firearms and survival.

Field identification & locations

Identify in the field by its glass-like, curved (conchoidal) fractures and its ability to scratch glass. Commonly found as nodules within limestone or chalk beds.